1. Technical Field of the Invention
This invention relates to a method for producing ceramics of a Si.sub.3 N.sub.4 -SiC system having a closed structure.
2. Prior Arts and Its Problems
It is known that ceramic having a Si.sub.3 N.sub.4 -SiC system has a defect that it has many open pores in the surface layer after sintering so that it has poor resistance to oxidation at high temperature and deteriorates various properties.
For preventing such deterioration of properties, for example, as disclosed in the Japanese Patent Publication No. 73907/1977, it has been proposed to close open pores by repeating the process which comprises impregnating pores with an organic silicon compound and subsequent heating.
However, even if SiC can be embedded into open pores by such process, Si.sub.3 N.sub.4 does not inter-react with SiC so that it is hardly possible to close the gap among Si.sub.3 N.sub.4. Accordingly, the deterioration of properties at high temperature cannot be prevented.